Strange metals and the phases of quantum materials

非技术总结该奖项支持理论研究，这些研究将研究量子物质的所谓“奇怪的金属”相，这种相在电子-电子相互作用非常强的系统中普遍存在。量子力学最初发展于二十世纪初，是作为单电子围绕氢原子核运动的理论发展起来的，但它也可以描述金属和半导体中大量电子的运动，这一描述对电子革命至关重要。在过去的几十年里，人们发现了无数的量子材料，其中量子力学的作用比人们之前认为的更深刻，也没有得到很好的理解。在量子材料中，重要的是统一处理电子的运动，并考虑不同电子之间的纠缠。在这些新材料中，最突出的是在一系列化合物中发现的高温超导体，这些化合物含有铜、氧和许多其他过渡金属，它们可以在相对较高的温度下导电而不会损失任何能量。在这个项目中，PI和他的团队将开发一种关于此类材料中电子运动的理论，特别是在电子运动与传统材料中最不同的温度和电子密度制度上。这一体系通常被称为“奇怪的金属”相，显然，电子的相互纠缠在揭示这一相的特殊性质方面起着重要作用。这个项目将建立在PI之前开发的一个模型的成功基础上，该模型提供了一个简单的设置，在这个设置中，电子之间的纠缠在某种意义上是最大的，但量子力学的方程可以精确地求解。PI和他的合作者最近将这个模型扩展到了一个更现实的环境，保持了它的可溶性，这产生了与对奇怪金属的观察相一致的令人鼓舞的结果。该项目将把对这种奇怪金属的理解扩展到量子材料的其他相，包括那些在高温下表现出超导电性的相，以及由一个原子厚的碳原子片以不同的配置堆叠在一起的微观结构。该奖项还将通过支持对理论凝聚态物理前沿课题的研究生和博士后助理的培训，为科学工作者的发展做出贡献。此外，PI将继续开展一项积极的计划，包括公开讲座、访谈、座谈和高级研究生学校的讲座。技术总结该奖项支持研究量子物质的“奇怪金属”相的理论研究，这种相普遍存在于关联电子系统中，特别是那些表现出更高温度超导的系统。对奇异金属相的完整、定量的理解对于量子材料理论的发展是至关重要的。PI和他的团队最近在一种奇怪金属理论上取得了进展，该理论具有简单、通用和广泛适用于各种相关材料的吸引人的特点。在这个项目中，该团队将进一步发展Sachdev-Ye-Kitaev模型和相关理论，并将结果与众多实验探测器进行定量比较。对于铜酸盐超导体来说，奇怪的金属相与各种相邻相有关，包括伪隙相、超导体相和电荷有序相。该项目的另一个重点领域是石墨烯微结构，将包括对纳米级石墨烯薄片的研究，以及它们展示Sachdev-Ye-Kitaev模型的非费米液体特征的方式。该奖项还将通过支持研究生和博士后助理在理论凝聚态物理前沿课题上的培训，为科学队伍的发展做出贡献。此外，PI将继续开展一项积极的计划，包括公开讲座、面试、座谈和高级研究生学校的讲座。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NONTECHNICAL SUMMARYThis award supports theoretical research which will examine the so-called "strange metal" phase of quantum matter, which is ubiquitous in systems in which the electron-electron interaction is very strong. Quantum mechanics was initially developed in the early twentieth century as a theory of the motion of a single electron around the nucleus of a hydrogen atom, but it can also describe the motion of a large number of electrons in metals and semiconductors, and this description was vital to the electronics revolution. The past few decades have witnessed the discovery of numerous "quantum materials" in which the role of quantum mechanics is more profound than previously thought and not well understood. In quantum materials, it is important to treat the motion of electrons collectively, and account for the entanglement between the different electrons. Most prominent among these new materials are the high temperature superconductors found in a series of compounds which contain copper, oxygen, and numerous other transition metals, which can conduct electricity without any loss of energy above a relatively high temperature. In this project, the PI and his team will develop a theory of electronic motion in such materials focusing especially on a regime of temperatures and electron density where the motion of electrons is most unlike those in conventional materials. This regime is often called the "strange metal" phase, and it is clear that the mutual entanglement of electrons plays an important role in bringing out the peculiar properties of this phase. This project will build on the successes of a model previously developed by the PI, which provides a simple setting in which the entanglement between the electrons is, in a sense, maximal, and yet the equations of quantum mechanics can be solved exactly. The PI and his collaborators have recently extended this model to a more realistic setting which maintains its solvability, and this yields an encouraging correspondence with observations on strange metals. This project will extend this understanding of the strange metal to other phases of quantum materials, including those exhibiting superconductivity at high temperatures and microstructures that consist of one-atom-thick sheets of carbon atoms stacked in various configurations on top of each other.This award will also contribute to the development of the scientific workforce by supporting the training of graduate students and postdoctoral associates in topics at the forefront of theoretical condensed matter physics. Furthermore, the PI will continue to pursue an active program of public lectures, interviews, colloquia, and lectures at schools for advanced graduate students.TECHNICAL SUMMARYThis award supports theoretical research which will examine the "strange metal" phase of quantum matter, which is ubiquitous in correlated electron systems, especially those that exhibit higher temperature superconductivity. A complete, quantitative understanding of the strange metal phase is essential to progress in the theory of quantum materials. The PI and his team have recently made progress on a theory of strange metals, which has the attractive features of being simple, universal, and broadly applicable across the range of correlated materials. In this project, the team will further develop the Sachdev-Ye-Kitaev model and related theories and compare the results quantitatively with numerous experimental probes. For the cuprate superconductors, the strange metal phase will be related to various neighboring phases, including the pseudogap, the superconductor, and the charge-ordered phases. Another focus area of this project is on graphene microstructures and will include studies of nanoscale graphene flakes and the manner in which they can exhibit signatures of the non-Fermi liquid of the Sachdev-Ye-Kitaev model. This award will also contribute to the development of the scientific workforce by supporting the training of graduate students and postdoctoral associates in topics at the forefront of theoretical condensed matter physics. Furthermore, the PI will continue to pursue an active program of public lectures, interviews, colloquia, and lectures at schools for advanced graduate students.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.